Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$235.32	8.478%	$255.2704	$255.27	$255.25	$255.30
Purchase #2	$24.49	5.417%	$25.8166	$25.82	$25.80	$25.80
Purchase #3	$227.57	10.103%	$250.5614	$250.56	$250.55	$250.60
Purchase #4	$121.32	6.829%	$129.6049	$129.60	$129.60	$129.60
Purchase #5	$119.62	13.240%	$135.4577	$135.46	$135.45	$135.50
Purchase #6	$94.44	5.290%	$99.4359	$99.44	$99.45	$99.40
Purchase #7	$18.52	12.813%	$20.893	$20.89	$20.90	$20.90
7 purchase totals =	$841.28		$917.0399	$917.04	$917.00	$917.10